A Deriaz turbine is a type of water turbine similar to a Kaplan turbine but which has inclined blades to make it more suitable for higher heads. It is particularly suitable for the head range between 20 meters and 100 meters – a window of operation between that of the Kaplan and Francis turbine. Because the runner blades are adjustable, the Deriaz design offers a number of other advantages: (1) smooth and efficient operation over a wide range of head and load; (2) uniform distribution of pressure and load across the blade (i.e., from the casing to the mid-span to the hub); (3) freedom from development of cavitation across the entire operating range.

The Deriaz turbine is classified as a double-regulated, reaction, mixed-flow turbine. It is named after its inventor Paul Deriaz, a hydraulic designer, and was the first kind of diagonal turbine to be developed. An early major Deriaz turbine system was installed at plants on both the Canadian and U.S. sides of Niagara Falls.